Photometry is an important analytical method with various applications. The current state of the art photometric apparatus is usually a bench top instrument. Photometers can be divided into two groups, instruments using cuvettes and instruments using an immersible sensor. Cuvette based instruments are usually heavy desktop instruments, or smaller portable instruments with reduced functions. Most instruments using immersible sensors are comprised of a desktop unit connected to the immersible sensor via a light guiding glass fiber. The sensor is usually made from metal and or glass. Light originating in the desktop unit is guided through the sensor and passing a defined length of sample volume, then guided back into the desktop unit to a detector. Sensors are bulky and need to be cleaned before transfer into another sample.
Trau and Orban (DE 10149879) describe a handheld photometer using a disposable and immersible sensor tip with a cuvette recess function. In contrast to other instruments, a fraction of the optical path is an integral part of the disposable tip made from polymers. The advantage of this configuration is that sample contamination and sample cross contamination can be totally ruled out by exchanging a new tip for each measurement. The tip of DE 10149879 however has the disadvantage of a long optical path length the light has to travel through the tip material, resulting in low transmission. A characteristic feature of the tip of DE 10149879 is that the tip is partly immersed into the measurement solution and all parts of the hand held photometer are above the meniscus of the measurement solution. The liquid to be analyzed is then flowing into the optical recess of the tip which is acting as a cuvette. The tip of DE 10149879 also needs a reflective surface such as a metallic surface adding complexity and cost. The current invention overcomes several limitations by providing a photometric measurement tip using different types of light propagation.